Talk on the ship was that they were flying through the heart of a storm. Normally an airship pilot would apply several strategies to mitigate any damage to the ship and passengers and it seems like the pilot had already used up most of his options.
He tried everything to avoid the flow of the thunderstorm by going above it at first, which seemed to be working until he encountered another storm so he tried going below it, that too worked fine until somehow the two storms met up in the air, creating this huge perfect storm and there was simply no going around it and nowhere to land since they were at sea.
Such an occurrence where the airships avoided two storms only to have these two storms combine to form an even larger more violent storm was very rare. The fact that Zyra and her team had the misfortune to be traveling during the eye of the storm may be what saved their lives.
